1. Field of the Invention
This invention relates to a process for producing ethylene glycol mono-tert-butyl ether from ethylene glycol and isobutylene and, more particularly, to a process of conducting the above-described reaction by adding ethylene glycol di-tert-butyl ether to the reaction system.
2. Description of the Prior Art
Ethylene glycol mono-tert-butyl ether is a useful material exhibiting excellent properties as a solvent, dispersing agent, diluent, or the like in the field of paints and ink. It is well known that ethylene glycol mono-tert-butyl ether can be synthesized from isobutylene and ethylene glycol by reacting them in the presence of an acid catalyst. In addition, it is also known from, for example, U.S. Pat. No. 3,317,483, 3,170,000, 2,480,940, Japanese Patent Application (OPI) No. 82004/75 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") that strongly acidic cation-exchange materials are effective as the catalysts.
However, in producing ethylene glycol mono-tert-butyl ether from isobutylene and ethylene glycol, the use of these catalysts has failed to eliminate formation of an ethylene glycol di-tert-butyl ether by-product. Formation of the by-product ethylene glycol di-tert-butyl ether (abbreviated DBE) results in reduction in the yield of ethylene glycol mono-tert-butyl ether (abbreviated MBE), which is economically disadvantageous for the production of the end product. Thus, it has been desired to develop a process of suppressing formation of the by-product di-tert-butyl ether.
No processes have so far been discovered which effectively suppress formation of the by-product DBE in the etherification reaction between isobutylene and ethylene glycol.
As indicated above, three U.S. Patents teach that ethylene glycol mono-tert-butyl ether can be synthesized from ethylene glycol and isobutylene. Of these, U.S. Pat. No. 3,170,000 relates to a process of producing MBE from an olefin mixture containing isobutylene and alcohol, and selectively separating and recovering tert-olefin by the decomposition of the resulting MBE. This patent describes recycling a mixture of alcohol and MBE obtained in the final step to an etherification reactor in the first step. Also, Japanese Patent Application (OPI) No. 29413/76 describes the process of producing ethylene glycol mono-tert-butyl ether from ethylene glycol and isobutylene by previously adding ethylene glycol mono-tert-butyl ether to the reaction system. However, these processes suffer from the problem that the amount of by-product ethylene glycol di-tert-butyl ether further increases.